Wavemill: a new Mission Concept for High-­Resolution Mapping of Total Ocean Current Vectors
Christine, Gommenginger¹; Marquez, Jose²; Richards, Byron³; Caparrini, Marco²; Chapron, Bertrand⁴; Cotton, David⁵; Buck, Chris^6
1National Oceanography Centre, UNITED KINGDOM; ²Starlab, SPAIN; ³Astrium, UNITED KINGDOM; ⁴Ifremer, FRANCE; ⁵SatOC, UNITED KINGDOM; ⁶ESA, NETHERLANDS

The demand for ocean current measurements from space has never been greater: from the needs to optimise ship routing, ensure health and safety at sea, monitor pollutant dispersal or assist the selection of sites for tidal energy farms, the list of applications is endless. For research too, high-­‐ resolution maps of ocean currents are now needed to advance our understanding of oceanic dynamics, mixing and exchanges between water masses and how these physical processes impact air-­‐sea exchanges, oceanic productivity and marine ecosystems. Wavemill is a new mission concept driven by these scientific and operational needs. Based on the principle of hybrid interferometric SAR, Wavemill seeks to deliver high-­‐resolution high-­‐accuracy maps of the ocean surface current speed and direction. Because the instrument senses directly the displacement of the ocean surface, Wavemill estimates the total ocean surface current, including ageostrophic current components. As Wavemill is sensitive to ocean surface roughness, it will be possible to derive secondary products for ocean winds and waves. In addition, some information about sea surface topography may also be retrieved. While the details of a Wavemill spaceborne mission and of its performance are still under investigation, the goal is to deliver current vector maps over two swaths of 100 km each, with a resolution of 1 km or better. In this paper, we present preparatory activities currently underway to explore Wavemill's potential as a future spaceborne mission. The paper gives a brief review of the scientific and operational drivers for the mission, highlighting the synergy and complementarity with other initiatives and satellites, such as GlobCurrent, the Sentinels and the Surface Water and Ocean Topography (SWOT) mission. The paper outlines the technical activities that are being undertaken to identify critical issues and to quantify the capabilities of a spaceborne instrument, particularly regarding the effect of wind and waves on ocean current retrieval performance. We will consider the various means at our disposal to validate ocean surface currents from Wavemill against established current measurements and the challenges this raises. Finally, we outline how various scientific and operational requirements are driving the specifications of the Wavemill instrument and the characteristics of a potential future spaceborne mission.